Satellite DNA's and other simple, tandemly repeated nucleotide sequences are present in or about the centromeric heterochromatic regions of the chromosomes of man and numerous other eukaryotes. Their functions are unknown. We seek support to continue our studies of satellite DNA's in Drosophila. We will employ established biochemical, genetic and cytological procedures to extend our investigation of satellite DNA's and chromosomal proteins. The proposed experiments may provide information about: 1) the possibility that Drosophila satellites are compacted into centromeric heterochromatin in phosphorylated H1 histones; 2) the arrangement of satellite DNA sequences along the chromosome: 3) the effect of H1 phosphorylation on the in vitro preference of H1 histones for satellite DNA's in D. virilis; 4) the possible effects of phosphorylation on the conformation of Drosophila H1 histones; 5) the evolutionary relationships among the satellites of D. virilis, D. novamexicana, and D. melanogaster; 6) the chromosomal distribution and possible function of an unusual acid-soluble protein isolated from Drosophila nucleosomal core particles. Since satellite DNA's and H1 histones are chromosomal features common to Drosophila and to man, there is an excellent possibility that these experiments will provide information applicable to the problem of the organization and molecular architecture of human chromosomes.